The invention relates to a low temperature polysilicon (LTPS) TFT-LCD, and more particularly to a stacked storage capacitor structure and methods for fabricating the same.
FIG. 1A is a plan view of a pixel in which a storage capacitor for a conventional LTPS TFT-LCD is formed. FIG. 1B is a sectional view taken along line A-A′ of the pixel shown in FIG. 1A. FIG. 1C is an equivalent circuit of the pixel shown in FIG. 1A.
In FIG. 1A, a pixel 10 with a storage capacitor 12, a TFT 14 and a pixel electrode 140 disposed thereon is provided. A signal line 16 and a gate line 18 cross in the vicinity of the TFT 14, and are disposed around the pixel 10. The pixel electrode 140 and the storage capacitor 12 are electrically connected to the TFT 14 by means of via 146.
In FIG. 1B, a processed substrate 104 comprising a buffer layer 108, a p-Si layer 112 as a first conductive layer, a gate insulating layer 116, a second conductive layer 120, a first interlayer dielectric 124, and a second interlayer dielectric 128 is provided. The p-Si layer 112, the second conductive layer 120 and the gate insulating layer 116 therebetween consist of the storage capacitor (Cst)12. By means of well known processes, a metal layer 132 is formed. Thereafter, a passivation layer 136 with via 146 therein is formed over the metal layer 132 and the second interlayer dielectric 128. A transparent pixel electrode 140 is conformally formed over the passivation layer 136 and the via 146. The pixel electrode 140 may comprise ITO or IZO. Additionally, a backlight module 148 is disposed on the other side of the substrate 104, thus, a TFT array substrate 100 for a LTPS TFT-LCD is obtained. The arrow 144 represents light from the backlight module 148.
In FIG. 1C, an equivalent circuit of the pixel shown in FIG. 1A is provided.
To meet the increased requirements the higher display resolution, pixel size must be decreased, thus, the area of the storage capacitor used in LTPS TFT-LCDs must be minimized concurrently. As the display resolution increases, however, the area available on each pixel for the storage capacitor must be reduced to maintain aperture ratio. At the same time, problems such as flickering, image retention and cross-talk are likely to occur.
Accordingly, a new structure capable of increasing storage capacitance without sacrificing the aperture ratio of a pixel, or maintaining the storage capacitance while increasing the aperture ratio of a pixel in an LTPS TFT-LCD is desirable.